The present invention relates to a molding die and, more particularly, to a molding die used for manufacturing a cooling fan to be used in an automobile radiator, a condenser and the like.
In general, the molded article such as a fan is manufactured in such a manner that the center of gravity thereof coincides with the center of rotation thereof. If the center of gravity does not coincide with the center of rotation, such the molded article must be subjected to balance adjustment.
As means for adjusting the balance of such molded article it has been known to form a by adjusting a rugged portion in a molding die as disclosed in Japanese Utility Model Unexamined Publication Nos. 49-11066 and 50-102971 or to form a balance-adjusting projection on the molded article as disclosed in Japanese Utility Model Unexamined Publication Nos. 48-62607 and 50-61403.
According to such method of adjusting the balance of the molded article, when the center of gravity is unbalanced, a weight corresponding to the shortage is added to the light-weight side of the molded article so as to make the center of gravity coincide with the center of rotation, thereby eliminating the imbalance.
The quantity of unbalance of the molded article on a plane perpendicularly intersecting the axis thereof is generally expressed by two components including "direction" and "magnitude". The "direction" component can basically be expressed by a vector, with an unspecified magnitude, extending in a direction from the center of rotation towards the center of gravity of the fan. The "magnitude" can be expressed as a vector being a product of the weight of the fan and the distance between the center of gravity and center of rotation.